“The most dangerous time for a collision is when you pass through the plane of Pluto’s equator and when you pass all the other satellites,” the mission’s project scientist, Hal Weaver, told Wired. Satellites, in this use, means any rocky debris around the planet.

After an 18-month review that was published in 2013, NASA’s New Horizons team identified the most likely thing that would derail the entire Pluto mission: dust and debris.

And once the craft gets knocked off its course, Hersman told Wired, the entire vehicle could be destroyed — it has no recourse to get back on the right path.

When New Horizons launched back in 2006, only three of Pluto’s five moons were known to exist. The Hubble Space Telescope found two of the three merely two and a half months before New Horizons launched. This presents a logistical challenge for the vulnerable craft. The more moons that are nearby, the more targets there are for space rocks originating from the nearby Kuiper Belt to smash.

Any smashing means the creation of even more space rocks. The bits of dirt and rock that ricochet off the moons as a result of space rock collisions will then be floating around — dangerously in New Horizon’s path.

Alan Stern, principle investigator of the New Horizons team, isn’t too worried. He told AFP that “there is a one in 10,000 chance that the spacecraft could be lost in a collision with debris around Pluto.”

NASA announced on July 1 that, after 7 weeks of searching for anything that could come in the way of New Horizons’ path — dust clouds, rings or any other obvious threats — the path seems to be mostly clear, as far as they could tell, and they made the decision for New Horizons to stay on its predetermined course.

Other than a momentary blunder on July 4 — in which the spacecraft lost communication with Earth for a frightening 90 minutes — the mission has had smooth sailing. But if this glitch happens again, mission scientist Andy Cheng told the Washington Post, the whole mission could be lost.

And Stern says that the mission is not completely out of the woods.

“While I don’t lose sleep over this, the fact is, tomorrow evening is going to be a little bit of drama,” Stern told AFP. “Until we pass that point … we won’t really know with certainty that we cleared the system and that there were no debris strikes.”